1. Field of the Invention
The present invention relates to an image forming apparatus, a method of controlling operations of removing air bubbles and a computer readable information recording medium, and relates to operations of removing air bubbles in an image forming apparatus having a recording head that discharges liquid droplets.
2. Description of the Related Art
An image forming apparatus can be, for example, a printer, a facsimile machine, a copier, a plotter, or a multi-function peripheral in which some functions of a printer, a facsimile machine, a copier, a plotter, and so forth, are combined. As such an image forming apparatus, an ink jet recording apparatus is known, for example. An ink jet recording apparatus is known as an image forming apparatus of a liquid discharge recording type using a recording head that is configured as a liquid discharge head (or a liquid droplet discharge head) that discharges ink droplets. In such an image forming apparatus of the liquid discharge recording type, ink droplets are discharged by a recording head onto a sheet of paper that has been conveyed, so that an image is formed on the sheet of paper. The sheet of paper may include not only paper but also an OHP (Over Head Projector) sheet or such. Further, any thing capable of liquid being adhered thereto may be used as the sheet of paper. The sheet of paper may also be referred to as a recording medium, recording paper, or such. Forming an image may also be referred to as recording, printing or such. Image forming apparatuses of the liquid discharge recording type include a serial-type image forming apparatus and a line-type image forming apparatus. The serial-type image forming apparatus is such that a recording head moving in a main scan direction discharges liquid droplets and forms an image. The line-type image forming apparatus is such that a line type recording head is used where the recording head not moving discharges liquid droplets and forms an image.
It is noted that in the present patent application, an “image forming apparatus” of the liquid discharge recording type means an apparatus that discharges liquid to a medium such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, ceramics or such. “Forming an image” means not only giving to a medium an image that has a meaning such as a letter, a figure or such, but also giving to a medium an image that does not have a meaning such as a pattern or such (also means merely causing a liquid droplet to land on a medium). “Ink” means not only one called “ink” but is used as a general term of any thing that is capable of being used to form an image and may be referred to as recording liquid, fixing solution, liquid or such. For example, a DNA sample, resist, pattern material, resin, and so forth, are included in “ink”. Further, an “image” is not only a planar image but also an image given to a thing that has been formed three-dimensionally, or a statue or such having a three-dimensional shape formed as a result of being molded three-dimensionally or so.
For such an image forming apparatus, it is known to provide an arrangement where an ink supply system is provided to have a distribution member that distributes ink to plural heads, a circulation pump is used to circulate the ink from the distribution member, and the circulated ink is returned to the distribution member after being deaerated (see Japanese Laid-Open Patent Application No. 2010-131959).
However, when ink in which air bubbles are mixed is continuously circulated by a circulation pump, the air bubbles may be dissolved in the ink as finer bubbles, and then, may not positively be separated from the ink in an air-liquid separation tank (deaeration unit). As a result, when the ink is returned to the distribution member, the ink in which the air bubbles are dissolved may be fed to the heads, and thereby, a failure in discharging the ink may occur in the heads. Further, when air bubbles are to be removed from ink in which the air bubbles are dissolved, an amount of the ink that is discharged together with the air bubbles may be increased.